Small Heater Recommendations?

So I got my wife the original version of this 3 gallon aquaponics kit: https://backtotheroots.com/products/watergarden

We've got it set up and pumping, with a very small (throttled) air supply to keep the betta entertained with a tiny trickle bubbles out of "Mount Wannahockaloogie". We plan to add a nerite snail or two as we transition from wheatgrass and alfalfa sprouts to cilantro and basil that need more light and generate more alge.

THE QUESTION: Can anyone recommend a small reliable (won't overheat) heater for a 3 gallon tank? (I know, 3 gallons is slightly small, but it's the size for the aquaponics kit.)

Oh yeah: We keep the HVAC set to, and the room temp, between 72-74 all the time anyway, for us and our tropical Caique Parrot.